Semiconductor laser diode and method of manufacturing the same

ABSTRACT

Provided are a semiconductor laser diode and a method of manufacturing the same. The semiconductor laser diode includes a lower cladding layer disposed on a substrate; a ridge including an optical waveguide layer, an active layer, an upper cladding layer, and an ohmic contact layer, which are sequentially stacked on the lower cladding layer, and having a predetermined width, which is obtained by performing a channel etching process on both sides of the ridge; an oxide layer disposed on surfaces of the upper and lower cladding layer to control the width of the ridge; a dielectric layer disposed on left and right channels of the ridge; an upper electrode layer disposed on the entire surface of the resultant structure to enclose the ridge and the dielectric layer; and a lower electrode layer disposed on a bottom surface of the substrate. The method is simpler than a conventional process of manufacturing a semiconductor laser diode. Also, by controlling a wet oxidation time, the width of a ridge can be freely controlled and an ohmic contact layer can be automatically formed.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 2004-105818, filed Dec. 14, 2004 and Korean PatentApplication No. 2005-43466, filed May 24, 2005, the disclosure of whichis incorporated herein by reference in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to a deep ridge waveguide (RWG) laserdiode, which employs quantum dots as an active layer and is used foroptical communication, and a method of manufacturing the same, and morespecifically, to a semiconductor laser diode and a method ofmanufacturing the same, which can freely control the width of a ridgeand automatically form an ohmic contact surface by wet oxidation onportions of upper and lower cladding layers, so that the semiconductorlaser diode can be manufactured in an easier manner than theconventional method and improved in characteristics.

2. Discussion of Related Art

In general, a conventional RWG laser diode, which uses an active layeras a quantum well (QW) layer, includes a ridge on which an ohmic contactsurface is formed. In this case, since the ohmic contact surface shouldbe smaller in width than the ridge, the RWG laser diode can be degradedin characteristics.

In order to overcome such drawbacks, it is necessary to develop a newtechnique of minimizing the width of the ridge while maximizing thewidth of the ohmic contact surface when an RWG laser diode ismanufactured.

SUMMARY OF THE INVENTION

The present invention is directed to a semiconductor laser diode and amethod of manufacturing the same, which can freely control the width ofa ridge and automatically form an ohmic contact surface by performing awet oxidation process on portions of upper and lower cladding layers, sothat the semiconductor laser diode can be manufactured in an easiermanner than the conventional method and improved in characteristics.

One aspect of the present invention is to provide a semiconductor laserdiode including: a lower cladding layer disposed on a substrate; a ridgeincluding an optical waveguide layer, an active layer, an upper claddinglayer, and an ohmic contact layer, which are sequentially stacked on thelower cladding layer, and having a predetermined width, which isobtained by performing a channel etching process on both sides of theridge;

an oxide layer disposed on surfaces of the upper and lower claddinglayer to control the width of the ridge; a dielectric layer disposed onleft and right channels of the ridge; an upper electrode layer disposedon the entire surface of the resultant structure to enclose the ridgeand the dielectric layer; and a lower electrode layer disposed on abottom surface of the substrate.

Another aspect of the present invention is to provide a method ofmanufacturing a semiconductor laser diode including the steps of:sequentially forming a lower cladding layer, an optical waveguide layer,an active layer, an upper cladding layer, and an ohmic contact layer ona substrate; forming a ridge having a predetermined width bysequentially removing the ohmic contact layer, the upper cladding layer,the active layer, and the optical waveguide layer using a predeterminedphotoresist layer as an etch mask until a portion of the lower claddinglayer is exposed; forming an oxide layer on exposed surfaces of theupper and lower cladding layers; forming a dielectric layer on theentire surface of the resultant structure to enclose the ridge; removingthe dielectric layer to expose the ohmic contact layer; forming an upperelectrode layer on the entire surface of the resultant structure toenclose the ridge and the remaining dielectric layer; and forming alower electrode layer on a bottom surface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent to those of ordinary skill in the art bydescribing in detail exemplary embodiments thereof with reference to theattached drawings in which:

FIGS. 1A through 1D are cross-sectional views illustrating a method ofmanufacturing a semiconductor laser diode according to an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. This invention may, however, be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure is thorough and complete and fully conveys thescope of the invention to those skilled in the art. The same referencenumerals are used to denote the same elements.

FIGS. 1A through 1D are cross-sectional views illustrating a method ofmanufacturing a semiconductor laser diode according to an exemplaryembodiment of the present invention.

Referring to FIG. 1A, a lower cladding layer 110, a first opticalwaveguide layer 120 a, an active layer 130, a second optical waveguidelayer 120 b, an upper cladding layer 140, and an ohmic contact layer 150are sequentially formed on, for example, an InP (001) substrate 100.

In this case, the lower cladding layer 110 is an n-typeIn_(0.52)Al_(0.48)As layer, which is lattice-matched to the InPsubstrate 100, and may be formed to a thickness of about 1 to 2 μm,preferably, about 1.5 μm.

Each of the first and second optical waveguide layers 120 a and 120 b isan undoped In_(0.52)Al_(0.25)Ga_(0.23)As layer having a separateconfinement heterostructure (SCH) structure, which is lattice-matched tothe InP substrate 100, and may be formed to a thickness of about 130 to170 nm, preferably, about 150 nm.

The active layer 130 may be formed by repetitively forming InAs quantumdots and an undoped In_(0.52)Al_(0.25)Ga_(0.23)As barrier layer in 3 to7 cycles. The InAs quantum dots are spontaneously formed from InAs thatis (about 3.2%) lattice-mismatched to the InP substrate 100, and theundoped In_(0.52)Al_(0.25)Ga_(0.23)As barrier layer is lattice-matchedto the InP substrate 100. Here, the thickness of the barrier layer mayrange from about 15 to 30 nm.

The upper cladding layer 140 is a p-type In_(0.52)Al_(0.48)As layer,which is lattice-matched to the InP substrate 100, and may be formed toa thickness of about 1 to 2 μm, preferably, about 1.5 μm.

The ohmic contact layer 150 is a p-type In_(0.53)Ga_(0.47)As layer,which is lattice-matched to the InP substrate 100, and may be formed toa thickness of about 130 to 170 nm, preferably, about 150 nm.

Meanwhile, the lower cladding layer 110, the first and second opticalwaveguide layers 120 a and 120 b, the active layer 130, the uppercladding layer 140, and the ohmic contact layer 150 may be formed using,for example, a molecular beam epitaxy (MBE) apparatus or a metal organicchemical vapor deposition (MOCVD) apparatus.

Referring to FIG. 1B, a first SiN_(x) dielectric layer 160 is depositedon the ohmic contact layer 150 to a thickness of about 180 to 220 nm,preferably, about 200 nm, and a predetermined photoresist layer iscoated thereon.

Next, a photoresist stripe 170 is formed using, for example, aphotolithography process such that a ridge having a predetermined width“r” is formed.

Referring to FIG. 1C, by using the photoresist stripe 170 as an etchmask, the first dielectric layer 160 is etched to the same width as thephotoresist stripe 170 using, for example, a dry or wet etching process.Then, the photoresist stripe 170 is removed.

Thereafter, by using the remaining first dielectric layer 160 as an etchmask, the ohmic contact layer 150, the upper cladding layer 140, thesecond optical waveguide layer 120 b, the active layer 130, and thefirst optical waveguide layer 120 a are sequentially removed using, forexample, a dry or wet etching process, such that the lower claddinglayer 110 is exposed.

In order to form a deep ridge structure, the lower cladding layer 110may be etched to a predetermined thickness.

Here, the ridge structure refers to a central protruding portion that iscomprised of a portion of the lower cladding layer 110 and the remainingfirst waveguide layer 120 a, active layer 130, second optical waveguidelayer 120 b, upper cladding layer 140, and ohmic contact layer 150.

Referring to FIG. 1D, a wet oxidation process is carried out, forexample, in an H₂O atmosphere for about 1 to 7 hours at a temperature ofabout 480 to 520° C., preferably, about 500° C. Thus, Al oxide layers180 a and 180 b are formed on surfaces of the exposed upper and lowercladding layers 140 and 110, respectively.

In this case, an In_(0.52)Al_(0.48)As layer has an oxidation rate ofabout 162.5 nm/hr in a direction parallel to the InP substrate 100 andan oxidation rate of about 185.5 nm/hr in a direction vertical to theInP substrate 100, and the oxidation rate of anIn_(0.52)Al_(0.25)Ga_(0.23)As layer is about 1/100 the oxidation rate ofthe In_(0.52)Al_(0.48)As layer. Owing to a difference in Al content, theIn_(0.52)Al_(0.48)As layer is different in oxidation rate from theIn_(0.52)Al_(0.25)Ga_(0.23)As layer.

Accordingly, by controlling the wet oxidation time, when the activelayer 130 is much less oxidized than the upper and lower cladding layers140 and 110, it is possible to freely control the width “r” of theridge.

After the oxidation process, second SiN_(x) dielectric layers 190 a and190 b are deposited to enclose the ridge to a thickness of about 180 to220 nm, preferably, about 200 nm, and then removed using, for example, adry etching process until the ohmic contact layer 150 is exposed. Thus,an ohmic contact surface is automatically formed.

In this case, the dry etching process may be, for example, amagnetically enhanced reactive ion etching (MERIE) process.

Thereafter, an upper electrode layer 220 is formed of a p-type metal onthe entire surface of the resultant structure to enclose the ridge andthe second dielectric layers 190 a and 190 b. A bottom portion of theInP substrate 100 is lapped, and a lower electrode layer 210 is formedof an n-type metal on a bottom surface of the InP substrate 100. Thus, adeep RWG semiconductor laser diode according to the exemplary embodimentof the present invention is completed.

As described above, according to exemplary embodiments of the presentinvention, a wet oxidation process is performed on portions of upper andlower cladding layer of a deep ridge structure, so that the width of aridge can be freely controlled and an ohmic contact surface can beautomatically formed. As a result, the width of the ridge can besufficiently reduced, thus lowering the threshold current density andcontact resistance of a semiconductor laser diode. Therefore, thesemiconductor laser diode of the present invention can be improved incharacteristics and manufactured in an easier manner than theconventional method.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation. As for the scope of the invention, it is tobe set forth in the following claims. Therefore, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A semiconductor laser diode comprising: a lower cladding layercomprising InAlAs disposed on a substrate; a ridge including an opticalwaveguide layer, a quantum dot active layer, an upper cladding layercomprising InAlAs, and an ohmic contact layer, which are sequentiallystacked on the lower cladding layer, and having a predetermined width,which is obtained by performing a channel etching process on both sidesof the ridge, wherein the ridge also includes a portion of the lowercladding layer; an oxide layer formed by oxidizing surfaces of the upperand lower cladding layer to control an effective width of the ridge; adielectric layer disposed on left and right channels of the ridge; anupper electrode layer disposed on the entire surface of the resultantstructure to enclose the ridge and the dielectric layer; and a lowerelectrode layer disposed on a bottom surface of the substrate, whereinthe upper and lower cladding layers have a faster oxidation rate thanthat of the optical waveguide layer and active layer so that theformation of the oxide layer substantially changes the effective widthof the ridge without substantially changing the predetermined width ofthe active layer or the optical waveguide layer.
 2. The semiconductorlaser diode according to claim 1, further comprising an additionaloptical waveguide layer interposed between the active layer and theupper cladding layer.
 3. The semiconductor laser diode according toclaim 1, wherein the upper and lower cladding layers are a p-type InAlAslayer and an n-type InAlAs layer, respectively, which arelattice-matched to the substrate.
 4. The semiconductor laser diodeaccording to claim 3, wherein each of the upper and lower claddinglayers is formed to a thickness of about 1 to 2 μm.
 5. The semiconductorlaser diode according to claim 1, wherein the optical waveguide layer isan undoped InAlGaAs layer having a separate confinement heterostructure(SCH) structure, which is lattice-matched to the substrate.
 6. Thesemiconductor laser diode according to claim 5, wherein the opticalwaveguide layer is formed to a thickness of about 130 to 170 nm.
 7. Thesemiconductor laser diode according to claim 1, wherein the active layeris obtained by repetitively forming InAs quantum dots, which arespontaneously formed from InAs that is lattice-mismatched to thesubstrate, and an undoped InAlGaAs barrier layer, which islattice-matched to the substrate, in several cycles.
 8. Thesemiconductor laser diode according to claim 1, wherein the ohmiccontact layer is a p-type InGaAs layer, which is lattice-matched to thesubstrate.
 9. The semiconductor laser diode according to claim 8,wherein the ohmic contact layer is formed to a thickness of about 130 to170 nm.